package ace.cmp.id.generator.snowflake.impl;

import ace.cmp.id.generator.api.LongIdGenerator;
import java.util.AbstractMap;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.CompletableFuture;

/**
 * @author Caspar 使用雪花算法
 * 一个long类型的数据，64位。以下是每位的具体含义。
 * <br>
 * snowflake的结构如下(每部分用-分开):
 * <br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
 * <br>
 * （1）第一位为未使用
 * （2）接下来的41位为毫秒级时间(41位的长度可以使用69年)
 * （3）然后是5位datacenterId
 * （4）5位workerId
 * （5）最后12位是毫秒内的计数（12位的计数顺序号支持每个节点每毫秒产生4096个ID序号）
 * <br>
 * 一共加起来刚好64位，为一个Long型。(转换成字符串长度为18)
 */
public class SnowflakeImpl implements LongIdGenerator {

  // 下面两个每个5位，加起来就是10位的工作机器id
  private long workerId; // 工作id
  private long datacenterId; // 数据id
  // 12位的序列号
  private long sequence;

  public SnowflakeImpl(long workerId, long datacenterId) {
    this(workerId, datacenterId, 0);
  }

  public SnowflakeImpl(long workerId, long datacenterId, long sequence) {
    // sanity check for workerId
    if (workerId > maxWorkerId || workerId < 0) {
      throw new IllegalArgumentException(
          String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
    }
    if (datacenterId > maxDatacenterId || datacenterId < 0) {
      throw new IllegalArgumentException(
          String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
    }
    System.out.printf(
        "worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d,"
            + " sequence bits %d, workerid %d",
        timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);

    this.workerId = workerId;
    this.datacenterId = datacenterId;
    this.sequence = sequence;
  }

  // 初始时间戳
  private long twepoch = 1672502400000L;

  // 长度为5位
  private long workerIdBits = 5L;
  private long datacenterIdBits = 5L;
  // 最大值
  private long maxWorkerId = -1L ^ (-1L << workerIdBits);
  private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
  // 序列号id长度
  private long sequenceBits = 12L;
  // 序列号最大值
  private long sequenceMask = -1L ^ (-1L << sequenceBits);

  // 工作id需要左移的位数，12位
  private long workerIdShift = sequenceBits;
  // 数据id需要左移位数 12+5=17位
  private long datacenterIdShift = sequenceBits + workerIdBits;
  // 时间戳需要左移位数 12+5+5=22位
  private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

  // 上次时间戳，初始值为负数
  private long lastTimestamp = -1L;

  public long getWorkerId() {
    return workerId;
  }

  public long getDatacenterId() {
    return datacenterId;
  }

  public long getTimestamp() {
    return System.currentTimeMillis();
  }

  // 下一个ID生成算法
  public synchronized long nextId() {
    long timestamp = timeGen();

    // 获取当前时间戳如果小于上次时间戳，则表示时间戳获取出现异常
    if (timestamp < lastTimestamp) {
      System.err.printf("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp);
      throw new RuntimeException(
          String.format(
              "Clock moved backwards.  Refusing to generate id for %d milliseconds",
              lastTimestamp - timestamp));
    }

    // 获取当前时间戳如果等于上次时间戳（同一毫秒内），则在序列号加一；否则序列号赋值为0，从0开始。
    if (lastTimestamp == timestamp) {
      sequence = (sequence + 1) & sequenceMask;
      if (sequence == 0) {
        timestamp = tilNextMillis(lastTimestamp);
      }
    } else {
      sequence = 0;
    }

    // 将上次时间戳值刷新
    lastTimestamp = timestamp;

    /**
     * 返回结果：
     * (timestamp - twepoch) << timestampLeftShift) 表示将时间戳减去初始时间戳，再左移相应位数
     * (datacenterId << datacenterIdShift) 表示将数据id左移相应位数
     * (workerId << workerIdShift) 表示将工作id左移相应位数
     * | 是按位或运算符，例如：x | y，只有当x，y都为0的时候结果才为0，其它情况结果都为1。
     * 因为个部分只有相应位上的值有意义，其它位上都是0，所以将各部分的值进行 | 运算就能得到最终拼接好的id
     */
    return ((timestamp - twepoch) << timestampLeftShift)
        | (datacenterId << datacenterIdShift)
        | (workerId << workerIdShift)
        | sequence;
  }

  // 获取时间戳，并与上次时间戳比较
  private long tilNextMillis(long lastTimestamp) {
    long timestamp = timeGen();
    while (timestamp <= lastTimestamp) {
      timestamp = timeGen();
    }
    return timestamp;
  }

  // 获取系统时间戳
  private long timeGen() {
    return System.currentTimeMillis();
  }

  @Override
  public Long get() {
    return nextId();
  }

  public static void main(String[] args) {
    long start = System.currentTimeMillis();
    // 结果集
    Collection<AbstractMap.SimpleEntry<String, String>> list =
        new java.util.concurrent.LinkedBlockingQueue<AbstractMap.SimpleEntry<String, String>>();

    int execCount = 100000;
    List<CompletableFuture> completableFutures = new ArrayList<>(execCount);
    for (int i = 0; i < execCount; i++) {
      completableFutures.add(
          CompletableFuture.supplyAsync(
              () -> {
                return 1;
              }));
    }
    CompletableFuture[] completableFutureArray = new CompletableFuture[execCount];
    completableFutures.toArray(completableFutureArray);

    CompletableFuture.allOf(completableFutureArray).join();

    System.out.println("list=" + list + ",耗时=" + (System.currentTimeMillis() - start));
  }
}
